Another 30 aluminium orange disks with a 10 cm diameter were spread out for independent accuracy assessment (Fig. 1). Both types of ground control points (GCPs) could be easily identified on the collected imagery. Their exact locations were measured directly after UAV image acquisition using a Leica 1200 DGPS system in dual frequency real-time kinematic mode, providing centimetre positional and height accuracies (2–4 cm).